1. Field of the Invention
The present invention relates generally to spin valve sensors for magnetic heads, and more particularly to an improved Si seed layer for a PtMn spin valve sensor structure.
2. Description of the Prior Art
Increasing the areal data storage density of hard disk drives can be accomplished by reducing the written data track width, such that more tracks per inch (tpi) can be written on the disk, and/or by reducing the size of data bits, such that the number of bits per inch (bpi) on a data track can be increased. However, to read data from a disk with an increased bpi, it is also necessary to develop a sufficiently thin read gap within the read head of the magnetic head, such that unwanted magnetic field interference from adjacent data bits is substantially eliminated. Current state of the art magnetic heads have read head gaps of approximately 800 Å to 1,000 Å.
Magnetic heads for hard disk drives typically have a read head portion including a magnetoresistive (MR) spin valve sensor structure for reading data from the disk of the hard disk drive. As is well known to those skilled in the art, such MR sensor structures include a plurality of thin film layers disposed between two magnetic shields that define the read gap. The thin film layers have particular magnetic properties, and are sensitive to the magnetic field of the data bits on the hard disk. Thus, thinner layers disposed between the two magnetic shields will create a thinner read gap, which will allow the read head to detect the smaller data bits that a higher bpi data track contains. Additionally, where one or more of the sensor layers can be made thinner, the electrical insulation layers (G1 and G2) within the sensor can be made thicker, which reduces the incidence of electrical shorts through the G1 and G2 insulation layers.
The thin film layers of a typical MR spin valve sensor will include at least one antiferromagnetic layer, at least one pinned magnetic field layer, and at least one free magnetic field layer. When the magnetic field direction of the free magnetic field layer is parallel to the magnetic field direction of the pinned magnetic field layer, the electrical resistance R of the MR sensor is lowest. When reading data, a magnetic data bit of a hard disk will cause the magnetic field direction of the free magnetic field layer to change, whereupon the electrical resistance of the sensor increases. This change in resistance (ΔR) affects the electrical current passing through the sensor, which is thus detected as a data signal. The parameter ΔR/R is useful in comparing magnetic head performance.
It is therefore desirable to develop MR sensors having a decreased thickness, while maintaining or even increasing the ΔR/R value. Where the metallic MR sensor layers are made thinner, there is less shunting of electrical current through these layers and away from the free magnetic layer. This leads to an increase in ΔR and improved magnetic head performance. Another parameter that is significant in spin valve sensor performance is the free layer coercivity, and generally, the lower the coercivity, the more stable the MR sensor will be. Thus a thinner sensor that maintains coercivity or even decreases coercivity is desirable.
Many different materials have been utilized in the prior art in attempts to increase ΔR/R and reduce the coercivity of the MR sensor. The present invention relates to a MR spin valve sensor that is fabricated utilizing a particular seed layer that replaces the prior art Ta sublayer with a Si sublayer. This allows the use of a thinner PtMn antiferromagnetic layer, thus leading to a thinner MR sensor, which allows for thicker G1 and/or G2 insulation layers while maintaining the same read gap thickness.